1. Field of the Invention
The present invention relates to a semiconductor device, a process for producing the same, a carrier substrate and a process for producing the same.
2. Description of the Related Art
As small-sized electronic equipments, such as mobile phones or others, have been come into wide use, there has been a demand for minimizing the size and cutting the production cost of semiconductor devices to be installed in such electronic equipments. A conventional semiconductor device, wherein a semiconductor chip mounted onto a lead frame is resin-shielded, has a problem in that an area extending between inner and outer leads or a mounting area is relatively large. Further, in a BGA (ball grid array) type semiconductor device, there is another problem in that the production cost is high because it necessitates a substrate for mounting a semiconductor chip.
To minimize a size of a semiconductor device and to reduce a mounting area therefor, as well as to cut the production cost, a semiconductor device has been proposed, for example, in Japanese Unexamined Patent Publication (Kokai) No. 9-162348. The semiconductor device disclosed in Kokai No. 9-162348 includes a semiconductor chip mounted onto a chip-cementing resin, a resin package in which the semiconductor chip is shielded with epoxy resin, and a metallic film covering a resinous projection formed on a mounting surface of the resin package, which metallic film is electrically connected to an electrode section of the semiconductor chip by wire-bonding. This semiconductor device is advantageous in that inner and outer leads are unnecessary, contrary to the case wherein a lead frame is used, no substrate is necessary for mounting the semiconductor chip as in the BGA type packages, and the metallic film facilitates heat dissipation as well as eases the mounting operation of the chip onto the substrate because the metallic film has the same function as the connector terminals.
In the above-mentioned semiconductor device of a type wherein a high-frequency semiconductor chip is mounted, the mounting part metallic film on which the semiconductor chip is mounted is preferably used as a ground terminal for preventing noise from entering so that the electric properties are stabilized. Accordingly, it is necessary to electrically connect the ground terminal to the mounting part metallic film.
For example, in a semiconductor device 51 shown in FIG. 6, a mounting part metallic film 53 on which a semiconductor chip 52 is mounted and a connector part metallic film 54 electrically connected to the semiconductor chip 52 are partially extended at the side of the mounting surface. A ground connector part 55 is extended outward from a peripheral edge of the mounting part metallic film 53. A ground electrode of the semiconductor chip 52 and the ground connector part 55 are electrically connected to each other with a wire 56, and a signal electrode and the connector part metallic film 54 are electrically connected to each other with a wire 58.
To design the mounting part metallic film 53 as compactly as possible and to make a length of the wire 56 as short as possible, the ground connector part 55 is preferably provided as close as possible to the semiconductor chip 52. Thereby, there has been a demand for forming the mounting part metallic film 53 in a stepwise configuration. For forming the mounting part metallic film 53 in a stepwise configuration, a process for producing a carrier substrate for the production of the semiconductor device 51 will be described with reference to FIGS. 7(a) to 7(h), 8(a) and 8(b). In this regard, a process for forming the mounting part metallic film 53 will mainly be explained, while avoiding the illustration of the connector part metallic film 54 in FIGS. 7(a) to 7(b).
In FIG. 7(a), an etching resist (photosensitive resist) 61 is coated on the respective surfaces of a metallic substrate 60, such as a copper plate. Then, as shown in FIG. 7(b), the exposure and development are carried out while overlaying a photo-mask on the etching resist to result in a pattern 62 having a central vacant space of a required size (see FIG. 8(a)). Thereafter, as shown in FIG. 7(c), a first half etching is carried out (to remove approximately a quarter of the thickness of the metallic plate 60) so that a connector recess 63 is formed. In this regard, when the metallic plate 60 is a copper plate, ferric chloride is preferably used as the etching liquid. Subsequently, in FIG. 7(d), the etching resist 61 is stripped off to result in the connector recess 63 in the metallic substrate 60.
In FIG. 7(e), an etching resist (photosensitive resist) 61 is again coated on the metallic substrate 60 on which the connector recess 63 has been formed, and the exposure and development are carried out while overlaying a photo-mask on the etching resist in alignment therewith to result in a pattern 64 having a central vacant space of a required size (see FIG. 8(b)). Then, a second half etching is carried out (to remove an approximately quarter of a thickness of the metallic substrate 60) in FIG. 7(f) so that a mounting recess 65 is formed. Next, in FIG. 7(g), the etching resist 61 is stripped off to form the connector recess 63 and the mounting recess 65 having different thicknesses from each other in a stepwise configuration. In this regard, an area and a thickness of the half etching are freely adjustable by changing the design of the central vacant space pattern in the photo-mask.
Next, in FIG. 7(h), a multi-layered metallic film is formed, while coating the remainder of the metallic substrate 60 other than the connector recess 63 and the mounting recess 65 with a resist, not shown, by the electrolytic plating, vapor deposition or sputtering. Thus a carrier substrate 66 on which the mounting part metallic film 53 is formed in a stepwise configuration.
The repetition of the steps of coating the etching resist 61 onto the metallic substrate 60 and half-etching the same after being exposed and developed complicates the production process to increase the production cost. To form the first central vacant pattern 62 and the second central vacant pattern 64 of different sizes at a position aligned with each other, a highly accurate alignment is required, which causes the generation of many rejected products to lower the yield.
Accordingly, an object of the present invention is to provide a semiconductor device capable of being mass-produced at a low cost, a method for producing the same, a carrier substrate used therefor and a method for producing the same by solving the above-mentioned problems in the prior art to simplify the manufacturing process.
According to the present invention, there is provided a semiconductor device comprising: a semiconductor element having at least one signal electrode and at least one ground electrode; a mounting part metallic film having a bottom area on which the semiconductor element is mounted and a stepped area located at a periphery of the bottom area and being higher in horizontal level than the bottom area; a connector part metallic film spaced from the mounting part metallic film and arranged at a peripheral region thereof; electrical connecting means for electrically connecting the signal electrode of the semiconductor element to the connector part metallic film and connecting the ground electrode of the semiconductor element to the stepped area of the mounting part metallic film; and a resin for shielding the semiconductor element, the electrical connecting means, and at least mounting/connecting sides of the mounting part metallic film and the connector part metallic film.
At least one of the mounting part metallic film and the connector part metallic film comprises a four-layered film consisting of a gold layer, a palladium layer, a nickel layer and a palladium layer sequentially layered from a bottom.
According to another aspect of the present invention, there is provided a carrier substrate adapted to be used for producing a semiconductor device, the substrate comprising: a metallic base having at least one reference surface, a central recessed area and a stepped recessed area located at a periphery of the central recessed area, a depth of the central recessed area from the reference surface being greater than that of the stepped recessed area from the reference surface; the area; the metallic base also having a peripheral recessed area spaced from the stepped recessed area and arranged at a peripheral region thereof; a mounting part metallic film formed on the central recessed area and the stepped recessed area; and a connector part metallic film formed on the peripheral recessed area.
In the same manner as the above, at least one of the mounting part metallic film and the connector part metallic film comprises a four-layered film consisting of a gold layer, a palladium layer, a nickel layer and a palladium layer sequentially layered from the metallic base.
According to still another aspect of the present invention, there is provided a process for producing a carrier substrate comprising the following steps of: coating respective surfaces, including a reference surface, of a metallic base with etching resist; partially removing the etching resist on the reference surface of the metallic base so as to form a central vacant pattern, a ring-like vacant pattern at a periphery of the central vacant pattern, and a connection vacant pattern spaced from the ring-like vacant pattern; half-etching the metallic base by using the etching resist as a mask and side-etching a part of the metallic base between the central vacant pattern and the ring-like vacant pattern so as to form a mount recessed area including a central recessed area and a stepped recessed area located at a periphery of the central recessed area, a depth of the central recessed area from the reference surface being greater than that of the stepped recessed area from the reference surface and also to form a peripheral recessed area spaced from the stepped recessed area and arranged at a peripheral region thereof; forming a mounting part metallic film and a connector part metallic film on the mount recessed area and on the peripheral recessed area, respectively; and removing the etching resist from the metallic base.
According to further aspect of the present invention, there is provided a process for producing a semiconductor device comprising the following steps of:
(a) forming a carrier substrate;
(b) mounting a semiconductor element, having at least one signal electrode and at least one ground electrode, on the bottom area of the mounting part metallic film;
(c) electrically connecting the signal electrode of the semiconductor element to the connector part and connecting the ground electrode of the semiconductor element to the stepped area of the mounting part metallic film;
(d) shielding, with a resin for shielding the semiconductor element, the electrical connecting means, and at least mounting/connecting sides of the mounting part metallic film and the connector part metallic film so as to form a shielded part; and
(e) removing the shielded part from the carrier substrate together with the mounting part metallic film and the connector part metallic film.
A process further comprising a step for forming a stud bump on at least one of the mounting part metallic film and the connector part metallic film of the carrier substrate, after the semiconductor element is mounted on the bottom area of the mounting part metallic film.
The shield part is removed from the carrier substrate by etching the metallic base. Otherwise, the shield part is removed from the carrier substrate by peeling the shield part off the carrier substrate.